In the related application the printer system includes a control using two independently operating microprocessors. One microprocessor is dedicated to the operation and control of the printing unit while the other microprocessor controls the operation of the carriage drive, ribbon drive and other non-printing units. The non-printing units are controlled by the microprocessor through an interface or control elements which are programmable for operation in accordance with the distinctively different operational patterns of the non-printing units. Communication between the microprocessor and the non-print units as well as other operating elements of the printer control system is through a system of interrupts each unit or its control having an assigned interrupt level. Normally the microprocessor gives priority for handling the control requirements to the higher level interrupt. However, certain functions on lower levels must be completed in their entirety before a higher level function regains control of the microprocessor. Such a condition might occur when ribbon drive reversal occurs. In that event, the ribbon drive interrupt preempts the microprocessor until reversal control has been initiated. In that event, a conflict can develop and certain conditions requiring satisfaction to the higher level unit can become lost resulting in a malfunction of the higher level unit.